The present invention relates to the processing equipment for the fabrication of semiconductor-based devices. More particularly, the present invention relates to improved techniques for confining and controlling the pressure of the plasma in plasma processing chambers.
In the fabrication of semiconductor-based devices (e.g., integrated circuits or flat panel displays) layers of material may alternately be deposited onto and etched from a substrate surface (e.g., the semiconductor wafer or glass panel). As is well known in the art, the etching of the deposited layer(s) may be accomplished by a variety of techniques including plasma-enhanced etching. In plasma-enhanced etching, the etching of the deposited layer(s) on the substrate takes place inside a plasma processing chamber. During etching, a plasma is formed from a suitable etchant gas source to etch areas of the deposited layer(s) on the substrate that are unprotected by the mask, leaving behind the desired pattern.
Among different types of plasma etching systems, those utilizing methods to confine the plasma to a volume immediately above the substrate have proven highly suitable for efficient production and/or for forming the ever-shrinking features on the substrate. An example of such a system may be found in commonly assigned U.S. Pat. No. 5,534,751, which is incorporated by reference herein. Although plasma confinement results in a significant improvement in the performance of plasma processing systems, current implementations can be improved. In particular, it is realized that improvements can be made in the control of the pressure of the confined plasma and the accessibility of the plasma processing volume for substrate transport.
To facilitate discussion, FIG. 1A depicts an exemplary plasma processing chamber 100, including confinement rings 102 as they are currently implemented. Within plasma processing chamber 100, the substrate 106 is positioned upon the lower electrode 104. The lower electrode 104 incorporates a suitable substrate chucking mechanism (e.g., electrostatic, mechanical clamping, or the like) for holding the substrate 106. The reactor top 110 incorporates an upper electrode 112 disposed immediately opposite the lower electrode 104. The upper electrode 112, lower electrode 104, and confinement rings 102 define the confined plasma volume 116. Gas is supplied to the confined plasma volume 116 by etchant gas source 114 and is exhausted from the confined plasma volume 116 through the confinement rings 102 and exhaust port 120 by a vacuum pump. With gas flowing and an appropriate pressure established within the confined plasma volume, a plasma is formed within this volume by application of RF power to the lower electrode by RF source 108 while grounding upper electrode 112. Alternately, as is well known in the art, the plasma may be formed by applying RF power to both lower electrode 104 and upper electrode 112, or by grounding lower electrode 104 and applying RF power to upper electrode 112.
The confinement rings 102 serve both to confine the plasma to the volume 106 and to control the pressure of the plasma. The confinement of the plasma to the volume 116 is a function of many factors including the spacing between the confinement rings 102, the pressure in the volume outside the confinement rings and in the plasma, the type and flow rate of the gas, as well as the level and frequency of RF power. For effective plasma confinement, the pressure outside the confinement rings 102 should be as low as possible, preferably less than 30 millitorr. Confinement of the plasma is more easily accomplished if the spacing between the confinement rings 102 is very small. Typically, a spacing of 0.15 inches or less is required for confinement. However, the spacing of the confinement rings also determines the pressure of the plasma, and it is desirable that the spacing can be adjusted to achieve the pressure required for optimal process performance while maintaining plasma.
Commonly assigned U.S. Pat. No. 6,019,060 entitled “Cam-Based Arrangement for Positioning Confinement Rings In A Plasma Processing Chamber” by Eric H. Lenz, issued Feb. 1, 2000, incorporated by reference, taught that the pressure drop across the confinement rings is approximately proportional to the expression 1/(X2+Y2+Z2) where X, Y and Z are the distances between confinement rings as shown in FIG. 1B. Lenz provided a single movable ring and a stationary ring (X=constant, Y+Z=constant in FIG. 1B). By adjusting the distances Y and Z by moving the single movable confinement ring, as taught by Lenz, a plasma pressure control range can be obtained. FIG. 2 illustrates the relative pressure predicted by the expression above obtained by moving a single ring for of various fixed gaps, X. The expression predicts a. control range of 67-100% can be obtained, as illustrated in FIG. 2, while experiments found the achievable range to be approximately one half those values. In many cases, a wider plasma pressure range is required to achieve optimal process results on various types of films and devices within the same processing system.
In addition, in the method taught by Lenz, the confinement rings 102 are constrained between the upper and lower electrode assemblies and thus can restrict access to the interelectrode space for loading and unloading of substrates. As shown in FIG. 1C, even with the confinement rings 102 lifted to their uppermost position, the access to the interelectrode space is limited to the gap W, which is the difference of the total interelectrode space less the combined thicknesses of the confinement rings.
It is desirable to provide an increased range of pressure control while maintaining plasma confinement. It is also desirable to provide confinement rings that greater facilitate placement and removal of the substrate from the plasma processing system.